Each year, about a million people visit the Worlds of Fun and Oceans of Fun theme parks in Kansas City, Missouri, most of them unaware of an even stranger attraction lying about 100 feet below. Down there, in a place called SubTropolis, is a bustling enterprise zone where some 55 businesses have set up shop. You can find everything from 100-pound sacks of coffee beans to original reels of Gone With the Wind and the U.S. Postal Service’s stash of hundreds of millions of commemorative stamps.

With 5 million square feet of leased warehouse, light-industry, and office space, and a network of more than two miles of rail lines and six miles of roads, SubTropolis is the world’s largest underground business complex—and one of eight or so in the area. To people along this stretch of the Missouri River, however, subterranean development also represents an innovative local way to save energy and reduce greenhouse-gas emissions.

In the 1960s, the Hunt Midwest company, which owns SubTropolis, began renting out space created by limestone mining. When the energy crisis hit in the 1970s, people came to appreciate the advantages of locating businesses underground. That rationale is even more compelling today. More energy in the United States now goes to heating and cooling buildings than to powering cars and light trucks. Underground, the constant ambient temperature leads to greatly reduced heating and air-conditioning demands—about 85 percent lower than for a building on the surface, according to Donald Woodard, the former director of underground planning at nearby Park University (which may be the only school to have such a position).

Vanguard Packaging, a SubTropolis firm that manufactures cardboard displays for retail stores, aims for a zero carbon footprint. “We have 380,000 square feet that we’re not heating or cooling,” says CEO Mark Mathes. He hopes to install a wind turbine on the surface that would generate as much electricity as the company consumes.

Since subterranean offices lack roofs, external siding, flooring, and the usual support structures, they require fewer energy-intensive construction materials like steel and aluminum. Moreover, the low permeability of the limestone and intervening layers of shale keeps goods and records dry—an attribute, no doubt, that inspired the Postal Service to store its stamps down there.

Underground, a business’s environmental impact can be smaller, explains John Carmody, the director of the University of Minnesota Center for Sustainable Building Research, because no trees or other plants need to be cut, nor wetlands filled, to make way for commerce or industry. Gains can be made in urban planning as well, Carmody says: “By putting more resources underground, you can preserve surface land and make a denser city.”

Of course, working underground has its quirks. The weather in SubTropolis, for example, is predictable: “overcast and mid-60s,” as habitués like to say. Employees don’t get to see the sky, but what they do see, after driving through a hole in the side of a hill to reach their offices, is an endless expanse of limestone—walls, ceiling, pillars, and floor—all painted white. (Most of the “streets” are named after geologic layers of limestone and shale.) A facilities manager compared working underground to being in a mall, but the cavernous expanse more closely resembles an oversize parking garage, with some 10,000 limestone support pillars laid out in a grid, 40 feet apart. Office humor has it that, instead of getting a corner office by way of promotion, you get a pillar.

More than 10 percent of the industrial space in greater Kansas City is located “down under,” covering about 25 million square feet—an area bigger than the downtown business district. Mining limestone for use in roadway construction and agriculture continues, with additional acreage carved out each year. The same sort of facilities exist in Kentucky, Pennsylvania, and Tennessee. But with 90 percent of the world’s subsurface office space—and 45 million additional square feet available for future occupancy in SubTropolis alone—Kansas City is in the vanguard, chipping away at the energy problem one chunk of limestone at a time.